Recently, a television camera tube using an amorphous thin film has been developed, but it has not yet succeeded in providing a sharp image. See The 12th Conference on Solid State Devices (Tokyo) 1980, Page 97 et seq. In U.S. patent application Ser. No. 259,221, filed on Apr. 30, 1981, a television camera tube is described using a target which is prepared by providing a blocking layer comprising an n-type amorphous silicon semiconductor and a photoconductive layer comprising amorphous silicon, usually having a conductivity (at 20.degree. C.-25.degree. C.) of less than 10.sup.-8 (.OMEGA. cm).sup.-1, coated on an electrically-conductive layer in the sequence listed. This application also discloses that the formation of a cover layer having an electron-retention action on the light-sensitive layer further increases the sharpness of images formed therewith.
However, when vidicon type camera operations are performed using a camera tube having a target of the blocking layer-photoconductive layer construction as described above which is prepared using amorphous silicon (hereinafter referred to simply as "a-Si") as a homojunction, visible light having wavelengths of 550 nm or less is absorbed by the blocking layer and the light-electricity conversion efficiency is limited. It has therefore been desired to make further improvements in order to obtain sharp images.